The present invention relates to a control unit for a hydraulic impact wrench. More particularly, the present invention relates to a control unit for a hydraulic impact wench where a pulsed torque is controlled with high precision. Even more particularly, the present invention relates to a control unit that permits particularly simple construction.
Referring to FIG. 4, a conventional control unit for an impact wrench includes a cylinder casing 51 containing a main shaft 52. Cylinder casing 51 is rotatively driven by an air motor (not shown). The distal end of main shaft 52 is adapted to be engage members to be torqued. An oil cylinder 53, is formed inside cylinder casing 51. The sectional contour of oil cylinder 53 consists of a pair of two circular arcs whose centers are displaced to slightly eccentric positions from the rotational center of main shaft 52. The two circular arcs are aligned with each other to form a generally elliptical configuration. Sealed portions 53a, 53b, 53c, and 53d are defined at substantially quadrisected positions on the inner circumferential surface of the oil cylinder 53. Sealed portions 53a, 53b, 53c, and 53d extend along the axial direction of the oil cylinder. Oil cylinder 53 is filled with hydraulic operating fluid (not shown). A proximal end portion of main shaft 52 is disposed in the oil cylinder 53 perpendicular to the plane of the drawing sheet of FIG. 4.
A blade groove 54, is defined by the site corresponding to the disposition of the proximal end portion of the main shaft 52 and the oil cylinder 53. A pair of blades 55, 55 are placed slidably in the blade groove 54.
Referring to FIG. 5, a spring 56 energizes blades 55,55 outwardly in the diametrical direction thereof to move the distal end portions of blades 55,55 into slidable contact with the inner circumferential wall of the oil cylinder 53. Seal portions 52a and 52b in the main shaft 52 are formed at positions perpendicular to the respective blades 55, 55.
Referring now also to FIG. 4, when cylinder casing 51 is rotatively driven by an air motor a relative rotating position, defined between the main shaft 52 and the oil cylinder 53, changes. When respective seal portions 52a, 52b of the main shaft, and the distal ends of respective blades 55,55, are in contact with the respective seal portions 53a, 53b, 53c, and 53d, a position shown in FIG. 5 is reached. When the position shown in FIG. 5 is reached, hydraulic operating fluid, contained on either side of the respective blades 55, 55, defines a high pressure chamber H. Low pressure chamber L, not containing hydraulic operating fluid, is defined opposite the high pressure chamber H with respect to blades 55, 55. The low pressure chamber L has a lower pressure than the high pressure chamber H. Containment of the hydraulic operating fluid produces a pulse of high pressure that rotatively acts upon a main shaft 52 to apply a pulsed torque condition to a member to be torqued. The same condition for the containment of hydraulic operating fluid, as described above, appears where the cylinder casing 51 rotates 180 degrees from the position shown in FIG. 5.
A bypass mechanism is arranged so that one torque pulse is produced per rotation of the cylinder casing 51. The communication path mechanism communicates pressure from high pressure chamber H to low pressure chamber L only under conditions where respective seal portions 53b, 53d, 52a, and 52b are in contact with each other.
After the high pressure chamber H and the low pressure chamber L are defined in the oil cylinder 53, a portion of the high pressure hydraulic operating fluid contained in the high pressure chamber H must be bypassed to the lower pressure chamber L to release cylinder casing 51 for further rotation. A bypass passage 57 is defined in the cylinder casing 51 for this purpose. A valve shaft insertion hole 58, is bored on the cylinder casing 51 facing the bypass passage 57. An adjustable valve shaft 59 is inserted into the insertion hole 58.
A communication path 60 on the valve shaft 59 allows hydraulic operating fluid to penetrate the bypass passage 57. The communication path 60 functions as a variable aperture where the flow passage area of communication path 60 changes through axial adjustment of valve shaft 59. The peak pressure pulse in high pressure chamber H is controlled by the adjustment of the flow passage area. Thus the pulsed torque is controlled by varying the flow passage area of the communication path 60. When the flow passage area is reduced, high peak pressure is produced and a high pulsed torque is obtained for the hydraulic pulse generation mechanism.
A mechanism for stopping automatically the operation of the hydraulic pulse generation mechanism when a predetermined pulsed torque is obtained includes a relief valve 61 mounted on a shaft end portion on the distal side of the valve shaft 59. Relief valve 61 includes a ball 62 which is pressed by a spring 63 into contact with a shaft end surface of valve shaft 59. Hydraulic operating fluid in communication path 60, acts upon ball 62 through a pressure leading path 64, defined in a shaft center portion of valve shaft 59, so that pressure opposes the force of spring 63.
A secondary side of relief valve 61 communicates with a cylinder chamber 65 on a top cover. A piston 66 is contained inside cylinder chamber 65. An automatic shut off mechanism (not shown) is operated by a movement of a piston 66 upon a rod 67.
As a result, during operation when a predetermined peak pressure is produced in the high pressure chamber H and hydraulic operating fluid in communication path 60 exceeds a predetermined pressure, relief valve 61 is opened against the force of spring 63. Thus, the hydraulic operating fluid is released to flow into the cylinder chamber 65 to push a piston 66 and operate the automatic shut off mechanism through rod 67. This ends the operation.
Pulsed torque in the hydraulic pulse mechanism is generated when valve shaft 59 is transferred axially to adjust the flow path area of communication passage 60. At the same time valve shaft 59 adjusts the spring force of spring 63 in relief valve 61.
When the pulsed torque is increased, valve shaft 59 is translated to the right side of FIG. 5 thus increasing the opening of the aperture in communication path 60. This increases the peak pressure of hydraulic operating fluid produced in high pressure chamber H. Simultaneously, spring 63 of relief valve 61 is compressed to set the relief pressure to a high value.
The pulsed torque is influenced by two related values, the peak pressure of a hydraulic operating fluid in high pressure chamber H, and the spring force in relief valve 61. When the peak pressure and the spring force repeat with the same characteristics as that of the original response to transfer of valve shaft 59 an operator achieves a similar torque. In a conventional hydraulic impact wrench, the peak pressure and the spring force are correlative but do not vary with quite the same characteristics. In hydraulic impact wrench operations where the spring force is more that the increase in peak pressure, relief valve 61 may not operate and thereby cause inconvenience to operators. In hydraulic impact wrench operations where a sufficient peak pressure is obtained, relief valve 61, may open before a predetermined peak pressure is obtained if a sufficient spring force is not achieved. This results in less than the desired torque for the operator.
Conventional pulse generation mechanisms are particularly disadvantaged by very high dimensional accuracy requirements and close attention to manufacturing and assembly details to achieve the desired precision torque control and reduce persistent failures to operate. Manufacturing and assembly details, for conventional pulse general mechanisms, require close attention to the selection of force constant in spring 56, the dimensional accuracy of valve shaft 59 and the assembly of respective members.
It is an object of the invention to provide a hydraulic impact wrench control unit structure that overcomes the foregoing problems.
It is a further object of the invention to provide a control unit where a fixed aperture is disposed at a position located nearer to a high pressure chamber than a branched section of a pressure leading path.
It is a further object of the invention to provide a control unit where a fixed aperture is disposed at a position located on a side nearer to a low pressure chamber than a branched section of a pressure leading path
According to an embodiment of the invention, there is provided a hydraulic impact wrench control unit comprising: a bypass passage, the bypass passage is defined between a high pressure chamber and a low pressure chamber, a pressure leading path is branched halfway through the bypass passage, a fixed aperture is disposed at a position located nearer to the high pressure chamber that a branched section of the pressure leading path, the pressure leading path is connected to a primary side of a relief valve, an automatic shut off mechanism is connectively linked by relieved hydraulic operating fluid that is disposed on a secondary side of the relief valve, the automatic shut off mechanism is constructed such that air supply to an air motor is stopped upon operation of the automatic shutoff mechanism, a relief pressure regulating means for regulating a relief pressure in the pressure relief valve is disposed between a primary side and a secondary side of the relief valve.
According to another embodiment of the invention, there is provided a a control unit further comprising: a fixed aperture , the fixed aperture being disposed at a position located on a side nearer to a low pressure chamber than a branched section of a pressure leading path is a bypass passage.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.